United’s version is rather more straightforward. Having followed Herrera for two years, they had concluded he was worth around £20m, their feeling being it would be another 18 months or so before he was a guaranteed first-team pick. Bilbao insisted they wanted the full amount, no compromise was reached and that would have been it finished, in United’s opinion, until the television pictures of Laffer’s representatives led to the inaccurate impression that an agreement was close – building up hopes for a deal that had already failed.

As reported by Christopher Atkins from the Bleacher Report, Herrera then explained that neither him nor his manager had spoken to United, following confirmation from Athletic Bilbao´s president that United would not be activating the release clause:

The only option, as the president said, was to pay my clause. I was never told United would pay the clause.
At no time have either I or my agent reached an agreement with United.

Jack De Menezes from The Independent confirms this adding quotes from Herrera:

It’s totally false that an agreement was reached with me. To talk with me they would’ve had to pay the clause.
I’m grateful for that and also because Athletic have not wanted to negotiate, as that shows how they value their players

This supports Manchester United´s story, although Herrera would of course never reveal in public if his agent had been secretly negotiating a deal with United.

Most often the simplest explanation is the correct one:

Manchester United bid for Herrera

Athletic Bilbao rejected the offer

Manchester United stopped bidding, not wanting to pay the full buyout clause (€36m)

Some persons tried to negotiate behind the curtains, hoping to make some money facilitating the deal

Reporters went batshit crazy over the whole matter, speculating about conspiracies that never happened